You will never get fired. Job security is great as the company rewards loyalty, not performance. If you are single, don't mind moving all over the country as your only promotion opportunity, don't mind spending most of your life in Texas, and you are very good at networking and kissing up to the executives, then you will fare well. If you live in a low cost of living state, the compensation is fairly good.

Cons

AT&T rewards who you know, not what you know. I've been told this face to face by more than one executive as I've had to turn down job opportunities that would have forced me to uproot my family. The company is extraordinarily not emergent in regards to modern workplace practices. The compensation is terrible if you live in a high cost of living area. Promotions are based on who your 'godfather' is, and absolutely not based on results or the bottom line revenue that you've brought in. I've had 5 supervisors, and not one of them has spent 5 minutes beyond the required time, to proactively help me with my career. Expectations are very low on performance. If you are looking for a challenge, don't work at AT&T. 90% the employees are stagnant and apathetic, and the remaining 10% are in it for themselves only. True intellectual, creative or innovative thought is not harnessed or appreciated. Although the company is huge, job movement or growth is minimal or non-existent (unless you have a godfather). Group think runs rampant, and lack of appreciation for new ideas or ways to take care of the customer are minimal. Support organizations, from my personal experience this includes legal, marcomm, tech support, and product teams) make it impossible to get anything done as you have to email three times to get a response, and then they only respond when you cc' their supervisor or an executive. This is the slowest moving, backwards, and stodgy company I've every worked for.